Vapor recovery system



March 4, 1969 J. T. WENTWORTH Re. 26,530

VAPOR RECOVERY SYSTEM Original Filed Jan. 27. 1964 i mm:

\zy. Z INVENTOR.

United States Patent 26,530 VAPOR RECOVERY SYSTEM Joseph T. Wentworth,Royal Oak, Mich., assignor to General Motors Corporation, Detroit,Mich., a corporation of Delaware Original No. 3,221,724, dated Dec. 7,1965, Ser. No. 340,298, Jan. 27, 1964. Application for reissue Dec. 5,1967, Ser. No. 698,064 US. Cl. 123-136 7 Claims Int. Cl. F02m 17/34Matter enclosed in heavy brackets appears in the original patent butforms no part of this reissue specification; matter printed in italicsindicates the additions made by reissue.

ABSTRACT OF THE DISCLOSURE This invention relates to a vapor recoverysystem for the fuel system of an internal combustion engine. Inparticular, gasoline vapors given off by the fuel tank and carburetor ofan engine while shut off are adsorbed temporarily by a vapor adsorbent,such as activated charcoal. When the engine is running the fuel vaporsare desorbed and conducted through the fuel system and burned in thecombination chambers of the engine.

Background of the invention- Vehicle hydrocarbon emissions contaminatethe atmosphere of cities at the rate of thousands of tons per day. Agood percentage of this contamination is believed to be due to gasolinevapors which escape from automobile carburetor and gasoline tank vents.With more and more passenger vehicles being put in use every day thisproblem is becoming more serious.

While a complete solution to the hydrocarbon emission problem requires aconsideration of vehicle exhaust gas discharges and other sources of airpollution, an important segment of the Whole problem is the evaporationof gasoline vapors from the fuel systems of automobiles. Hence, aninexpensive and effective solution to this problem would help to reduceair pollution.

It has been proposed to reduce the evaporation loss to the atmosphere bytrapping the escaping vapors on an adsorbent material, such as activatedcharcoal, attached to the vehicle fuel system vents. One of the firstquestions to be considered is whether the adsorbent material should belarge enough to accept all of the vapors for an indefinitely long periodof service, and then be discarded or exchanged, or whether a smalleradsorbent bed should be used which could be periodically reactivated orstripped of adsorbed vapors in normal use. Our experience has shown thatthe evaporation losses from the automobile fuel system, especially onhot days, can be of such magnitude that an adsorbent bed based on theformer approach would have to be prohibitively large.

A system utilizing the reactivation approach is disclosed in the UnitedStates Patent 3,093,124 issued June 11, 1963 to the assignee of thepresent invention.

In this system, vapors given off from the carburetor float bowl andgasoline tank while the engine is off are captured in an adsorbentcanister encircling the exhaust pipe. Each time the car is driven thecanister will be heated and the adsorbent material purged of the trappedfuel vapors. The desorbed vapors are piped to the engine intake manifoldand consumed. All vapors escaping from the carburetor or gasoline tankwhile driving bypass the adsorbent canister and are vented directly tothe intake manifold. Having been reactivated while driving, theadsorbent material will be ready to accept vapors during the nextshut-down period. Since this material need only Reissued Mar. 4, 1969hold vapors given off between trips, the bed may be much smaller thanthat required for a non-cycling type of adsorbent bed. Relatively hightemperatures are required to reactivate the canister when activatedcharcoal of the common gas-adsorbent type is used. These charcoals havethe largest possible number of small diameter pores to obtain maximumadsorptive capacity with high retentivity. However, the smaller poresnecessitate reaching temperatures of from 300 to 400 F. to drive theadsorbate off.

Summary of the invention The present invention is an improvement overthe above-described vapor recovery system.

Activated charcoal having a pore size distribution better suited to thecollection and desorption of gasoline vapors is now available. Thisimproved charcoal has more pore volume concentrated in somewhat largerpores than the usual gas-adsorbent charcoal, and may be reactivated attemperatures between F. and 250 F. Since reactivation is essential tothe scheme of retaining a compact size, the ease with which an adsorbentis reactivated is an important consideration in the design of a vaporrecovery system.

In accordance with this invention, a fuel vapor recovery system isprovided in which a low reactivating temperature adsorbent is used. Thismakes it possible to locate the adsorbent bed within the engine airintake passages leading directly to the intake manifold. When the engineis off, vent lines from the carburetor float bowl and the fuel tankdeliver raw gas vapor mixtures to the adsorbent Where they are acceptedand stored. When the engine is started, the air sucked through the airintake and carburetor is soon heated to the ambient underhoodtemperature of the engine compartment. This air passes through andaround the adsorbent bed heating it to its reactivation temperature thusdriving off the trapped fuel vapors. These vapors are carried to thecombustion chambers of the engine and burned. When the engine is againshut off, fuel vapor concentration beings to build up while theadsorbent bed is gradually cooling off. With proper design, vaporpressure build up can be matched with the size and shape of the bed sothat the adsorption process keeps pace with the evaporation rate.

Brief description of the drawing A better understanding of the inventionmay be had by referring to the following description and drawingswherein:

FIGURE 1 is a schematic view of a portion of an engine fuel systemincorporating the invention showing a typical carburetor and air cleanerasembly; and

FIGURE 2 is a fragmentary view of FIGURE 1, showing the condition of thevapor recovery system when the engine is running.

Description of the preferred embodiment Referring to FIGURE 1, a typicalcarburetor and air cleaner assembly 10 is shown. This assembly ismounted on the intake manifold 12 of an engine fuel system incorporatingthe inventive vapor recovery system generally designated by the numeral14.

The carburetor 15 has an air horn 16 containing a choke valve 18 and athrottle valve 20. A fuel well 22 connects through a discharge nozzle 23with the throat 24 of the air horn and contains a metered quantity ofgasoline 25 to be mixed with air passing the nozzle 23 and consumed inthe engine combustion chambers. An air filter 26 mounted on thecarburetor contains a paper filter element 28 located between the airborn 16 and the air cleaner intake 30.

The vapor recovery system 14 includes an adsorbent bed 32 located in theair intake of the air cleaner. The bed consists of an adsorbentmaterial, such as activated charcoal, and is mounted in a canister 29coaxially spaced from the walls of the slightly enlarged air intake sothat air can flow freely through and around it. Any suitable means ofsupport may be provided, such as sleeve 31. The ends of the canister areclosed with fine screens 33 which retain the adsorbent and allow someair to sweep through the bed when the engine is running.

FIGURE 1 shows the condition of the system when the engine is off. Avapor duct 34 leading from the bed 32 through sleeve 31 connects with avapor distribution valve 35 schematically represented here fordescriptive purposes. A rotatable valve element 36 having a T-shapedpassage 37 is illustrated as being operated through the linkage 38 by asolenoid 40 controlled by the ignition switch 42. Of course, othersuitable means may be used to control the valve 35 such as a diaphragmactivated by engine oil pressure. In the off position, the valve element36 connects the vapor duct 34 with the vent conduit 44 leading to thecarburetor fuel well 22 and with the vent line leading to the vehiclefuel tank. Hydrocarbon emission from these fuel storage areas willcontinue until the system is saturated at which time the efiluent vaporpressure causes penetration of the bed 32 and adsorption of the fuelvapors.

When the engine has just been turned off, the bed 32 will remain at afairly high temperature as a result of the previous trip and will beunable to adsorb any appreciable amounts of vapor. However, immediatelyafter engine shut-down very little vapor is given off and vaporconcentration is low. In time, the vapor concentration builds up, but bythis time the bed 32 will have cooled to the point where it can acceptand keep pace with the rate of evaporation.

When the engine is started the valve element 36 is rotated to theposition shown in FIGURE 2 by the solenoid 40 which is energized whenthe ignition switch 42 is closed. In this position the vent conduits 44and 45 are connected directly to the air horn 16 through bypass line 47and the vapor duct 34 is closed. Hence, fuel vapors in the fuel well 22and in the vehicle gas tank will be conducted into the carburetor throat24 and burned in the engine when it is running.

During this period of operation, air is drawn through the air intake 30of the air cleaner and passes through and around the bed 32. The wallsof canister 29 may be perforated to permit free air movement. This airis heated to the ambient underhood temperature of the engine compartmentand has sufficient latent heat to bring the temperature of the bed 32 toits reactivation temperature. This temperature is reached in a matter ofminutes and as a result, substantially all of the stored fuel vaporsaccepted during the shut-down period are given up in about 15 minutes.An important advantage over the system described in Patent 3,093,124 isthe air sweep effect. That is, vapor molecules are desorbed and becomeentrained in the moving air stream much faster than where a closedcanister is used and desorption vapor pressure is relied on to conveythe gases to the engine.

The desorption phase should be short, but not so rapid as to over-enrichthe fuel mixture. Also, since 15 minutes is about the average minimumtime required for most urban trips, it is assumed that the bed will bereactivated after nearly every run. The rate at which desorptionproceeds will depend primarily on the properties of the charcoaldesiccant, the temperature, and the air flow rate around the bed.Adjustment of these factors will result in a rate of desorption whichwill permit the reactivation of the bed in a reasonably short time andyet not cause undue richening of the airfuel mixture entering theengine. The bed location may be a matter of choice so long as it is inthe air stream moving to the carburetor. A location on the downstreamside of the filter element 28 may be desirable in preventingcontamination from dirt.

Experience indicates that there is an optimum range of pore sizes forgreatest adsorption of any hydrocarbon vapor. For a gasoline burningfuel system the most effective gas adsorbent charcoals should retain thehydrocarbons of 4 to 6 carbon number when mixed with air at aconcentration of about 10% by volume, It is expected that in actualservice the vapor concentration in a fuel system will be in this range.The size of the charcoal particles is not too critical, but I have foundthat the sieve fraction between 30 and mesh serves well.

Activated charcoal consists of tiny pores of various diameters. The porediameters found in gasadsorbent charcoals such as those used in thepresent invention may range from 5 Angstroms to many thousands ofAngstroms. The pore size distribution is determined primarily by the rawmaterial used and the method of activation. The smallest pores are themost active and are first filled. Less volatile adsorbates will displacethe more volatile which will then occupy larger diameter pores or bedesorbed altogether.

The smallest pores (up to about 20 Angstroms in diameter) hold vaporsmost tenaciously but increase the difficulty of desorption. Larger pores(from about 20 to 60 Angstroms) will still retain hydrocarbon vapors andthe vapors can be desorbed more easily, that is, at a lower temperatureor in less time or both. Pores larger than about 60 Angstroms are lesseffective in holding vapors of the kind vented from automobile fuelsystems.

Activated charcoal is now available which has a considerable portion ofits pore volume concentrated in the desired size range. For example,improved charcoal having a total pore volume of 1.53 ml./gram may havemore than 0.4 ml./gram in pores ranging from 20 to 60 Angstromdiameters. This charcoal can be reactivated at temperatures of from to250 E, which is within the range of air temperatures commonly found inthe underhood space of operating automobiles. In contrast, thistemperature range is considerably lower than the 300 to 400 F. rangefound necessary in the previously mentioned system disclosed in US.Patent 3,093,124. Other desiccants may be used such as activatedaluminas and bentonites, but activated charcoal having the abovecharacteristic is preferred.

Having now described my invention in detail and the most preferredembodiment thereof, it is clear that certain obvious modifications maybe made by those skilled in this art without deviating from the scope ofthe invention and expressed in the appended claims.

I claim:

1. A fuel vapor recovery system for the fuel system of an internalcombustion engine comprising,

a fuel-air mixture intake passage means for the engine,

a fuel reservoir,

air inlet means for the fuel-air mixture intake passage means includingan air cleaner assembly having air duct means and containing a filterelement therein,

fuel vapor adsorption means located in said air duct means and beingheated by the air stream moving within the air duct means when theengine is running to cause desorption of stored fuel vapors,

vent passage means leading from the fuel reservoir and connecting withthe vapor adsorption means,

a bypass passage means connecting between the vent passage means and thefuel-air mixture intake passage means,

valve control means associated with said engine, and

valve means responsive to said valve control means to close the bypasspassage means when the engine is not running and to close the ventpassage means when the engine is running so that fuel vapors from saidreservoir are temporarily accepted and stored by the vapor adsorptionmeans when the engine is off and are bypassed to the fuel-air mixtureintake passage means when the engine is running.

2. A fuel vapor recovery system for the fuel system of an internalcombustion engine comprising,

a carburetor having a throttle restricted throat and a fuel wellcommunicating therewith,

air inlet means for said throat including an air cleaner assembly havingair duct means and containing a filter element therein,

a fuel reservoir containing fuel to be consumed by the engine,

a gas-adsorbent activated charcoal bed located in said air duct means,said bed being heated by air moving in the air duct means and passingaround and through the bed when the engine is running causing desorptionof stored fuel vapors therein,

vapor distribution valve control means energized by the engine ignitionsystem,

vapor distribution valve means responsive to said valve control means todirect fuel vapors from said fuel well and reservoir to said charcoalbed to be accepted and stored therein when the ignition is off and todirect said fuel vapors directly to said carburetor throat when theignition is on,

a first vent passage leading from the fuel reservoir to said valve meansand communicating with said throat when the ignition is on,

a second vent passage leading from said fuel well to said valve meansand communicating with said throat when the ignition is on, and

a vapor duct leading from said charcoal bed to said valve means andcommunicating with said first and second vent passages when the ignitionis off.

3. A vapor recovery system according to claim 1 wherein said vaporadsorption means is activated charcoal having the maximum possiblenumber of pores with diameters of from to 60 Angstroms.

4. A vapor recovery system according to claim 1 wherein said vaporadsorption means has a pore volume of about 1.5 ml./gm., preferably withat least 0.4 mL/gm.

between 20 and 60 Angstroms.

5. A fuel vapor recovery system for the fuel-system of an internalcombustion engine comprising an intake passage for induction air flow tothe engine,

said intake passage having an air inlet,

a throttle valve disposed in said inlet for controlling induction airflow therethrough,

a fuel reservoir,

means for delivering fuel from said reservoir to the engine inaccordance with induction air flow through said air inlet,

an air cleaner assembly defining an air flow path, said air flow pathhaving its outlet in registration with said air inlet for said intakepassage, said air cleaner assembly having a filter element disposedacross said air flow path,

and fuel vapor adsorption means connected to said fuel reservoir wherebyfuel vapors from said reservoir may be temporarily accepted and storedby covery system for the fuel system of an internal combus tion enginehaving an intake passage for induction air flow to the engine, on airinlet for said intake passage and a fuel reservoir, said air cleanerassembly comprising means defining an air flow path, said air flow pathhaving its outlet arranged for registration with said air inlet for saidintake passage, a filter element disposed across said air flow path, andfuel vapor adsorbing means adapted for c nnection to said fuel reservoirwhereby fuel vapors from said reservoir may be temporarily accepted andstored by said adsorbing means when the engine is off, said adsorbingmeans being disposed within said induction air flow path whereby airflow through said path to said intake passage may cause desorption ofstored fuel vapors from said adsorbing means at rates corresponding tothe rates of induction air flow when the engine is running. 7. A fuelvapor recovery system for the fuel system of an internal combustionengine comprising an intake passage for induction air flow to theengine,

said intake passage having an air inlet, a throttle valve disposed insaid air inlet for controlling induction air flow therethrough, a fuelreservoir, means for delivering fuel from said reservoir to the enginein accordance with induction air flow through said air inlet, fuel vaporadsorbing means connected to said reservoir whereby fuel vapors fromsaid reservoir may be temporarily accepted and stored by said adsorbingmeans when the engine is off, and means for directing at least a portionof the induction air flow through said air inlet to said adsorbing meansfor desorbing fuel vapor from said adsorbing means whereby fuel vapormay be desorbed and directed to the engine at rates corresponding to therates of induction air flow.

References Cited The following references, cited by the Examiner, ar

LAURENCE M. GOODRIDGE, Primary Examiner.

